Electrical precipitation



Jan. 30, 1934. s. P. MILLER 1,945,061

ELECTRICAL PRECIPITATION Filed June 8, 1929 INVENTOR a EMA w ATTORNEYS Patented Jan. 30, 1934 PATENT OFFICE 1,945,061 ELECTRICAL PRECIPITATION Stuart Parmelee Mille r,

signor to The Barrett Englewood, N. J., as-

Company, New York,

N. Y., a corporation of New Jersey Application June 8, 1929. Serial No. 369,496

1 Claim. (01. 202-30) This invention relates to an improved method of treating hot gases containing entrained particles of a pitchy or resinous nature whereby the entrainedparticles are. removed from the gases, and includes apparatus for treating the gases.

It is known that entrained particles may be removed from gases by subjecting the gases to .reatment in an electrical precipitator. When gases containing entrained pitchy or resinous constituents are subjected to electrical precipitation at temperatures sufliciently high to distill or decompose the pitchy or resinous constituents entrained in the gases difficulty has-been experienced due to deposition of the entrained matter on the collecting electrodes of the precipitatori'ollowed by.distillation or decomposition of this entrained matter to form a deposit of a solid or coke-like nature. The formation of such a deposit on the collecting electrodes of a precipitator and accretion of the deposit by continued operation is a source of trouble due to the clogging of the tubes or break down of the high voltage due to arcing between the electrodes and this irregular coke or pitch deposit.

According to this invention, gases containing such pitchy or resinous particles are cleaned at a high temperature while the formation of such hard or coke-like deposits on the electrodes is prevented. The hot gases with the pitchy or resinous particles entrained therein are passed down thru the tubes of an electrical precipitator and before the gases enter the tubes a substance which is a solvent for the precipitate is sprayed into the gases in suflicient quantity to flush the walls of the tubes and prevent the accumulation or formation of a hard or coke-like deposit thereon. By a solvent I mean ,a substance which is miscible with the resinous or pitchy precipitate and forms a homogeneous mixture therewith. Although the invention may be applied to the treatment of various gases containing pitchy. or resinous constituents suspended therein, it is described herein more particularly as applied to the treatment of coke oven gases or other coal distillation or coal'carbonization gases.

Coke oven gases, for example, leave the coke ovens at such a high temperature that if the gases are passed thru an electrical precipitator at a temperature near that at which they leave the ovens, the pitch entrained in such gases, which is thrown out of the gases by the electrical discharge and remains on the tubes of hot gases down thru the tubes of the electrical precipitator and not up into the tubes, and spraying the gases with a solvent for the precipitate, such as pitch or tar which may be a light tar or tarry oi1, and passing the gases into the precipitator tubes with a suflicient quantity of solvent suspended therein to wash down the walls of the precipitator and prevent the formation of deposits thereon, the gases on entering the precipitator and being subjected to the electrical discharge are freed from both the pitchy constituents entrained therein and the solvent whichhas been suspended therein. The solvent thus precipitated onto the tubes in flowing down the tubes together with entrained impurities carried by the gases washes the tubes and keeps them clean.

The gases are passed down thru the precipitator tubes in order that the greater part of the suspended pitchy particles and particles of solvent will be thrown out from the gasesonto the upper part of the tubes near the opening thru which the gases enter the tubes. Regardless of whether the gases flow up thru the tubes of an electrical precipitator or down thru the tubes of an electrical precipitator, the greater portion of the entrained matter is precipitated from the gases soon after they enter the discharge zone of the precipitator; for example, in a certain type of precipitator with tubes ten feet in length, thirty-five percent of the total entrained matter may separate in the first foot'of the tubes and thirty percent in the second foot, leaving only a relatively small proportion of the entrained matter to be precipitated in the remaining length of the tubes. When the gases are passed down thru the tubes as contemplated by this invention, the greatest part of the solvent and other entrained matter is precipitated from the gases near the top of the tubes and in flowing down over the surfaces of the tubes prevents the accumulation of any soluble precipitate thereon and washes downany small middle of the precipitator tubes and the discharge from these electrodes causes the suspended particles to precipitate out of the gases on $0 the tubes which serve as collecting electrodes. The suspended matter which is removed from the gases collects in the bottom of the precipitator and may be drawn off in any suitable way and put to any suitable use.

In treating hot coke oven gases according to this invention, the gases are advantageously sprayed with tar or pitch and the gases may be sprayed with a tar or pitch containing oils which will be volatilized by the hot gases and enrich the gases in condensable constituents. This latter process presents a method of distilling tar or a low melting point pitch in the hot gases the distillate from which will be recovered by cooling the enriched gases. A blended distillate of. required composition may be obtained byproperly selecting the enriching medium and controlling the amount of enriching medium sprayed into the gases, etc. The enriching medium must be sprayed into the gases in a quantity sufilcient to provide the precipitation of enough undistilled residue from the gases on to the collecting electrodes to keep these electrodes washed clean.

I Any excess of spraying medium over this required minimum which is sprayed into the hot gases and distilled by the gases serves to enrich them in condensable constituents which are recovered as clean oils when the gases are cooled.

If, for example, hot coal distillation gases, such as fresh hot coke oven gases direct from the ovens, are sprayed with tarry oil obtained from the condensers of an ordinary coke oven battery and the gases are then passed down thru an electrical precipitator with the tarry oil or residue from incomplete distillation of the tarry oil suspended in the gases, the electrical discharge in the precipitator will cause the pitchy constituents normally contained in the gases together with the tarry oil or undistilled residue thereof, suspended in the gases, to be precipitated on to the collecting electrodes and together they will wash down the electrodes and prevent the accumulation of tar or pitch thereon and eliminate the possibility of subsequent distillation of such a tar or pitch deposit to form coke.

When it is desired to clean the gases without altering their composition, the gases before they enter the precipitator may be sprayed with pitchy material of approximately the same composition and temperature as that contained in the gases. The gases are sprayed with suflicient material to prevent the formation of a hard or coke-like deposit on the precipitator tubes. According to one advantageous way of accomplishing this, the precipitate which collects'in the bottom of the precipitator is collected and pumped to suitable spray means situated above the precipitator tubes, and used for spraying further gases. All entrained matter is removed from the gases in the precipitator without altering the composition of the gases by addition to or subtraction from the vapors carried by the gases.

Altough the invention is described herein more particularly as applied to coke oven gases or similar fresh hot coal distillation or coal carbonization gases, and is described in the drawing as applied to the treatment of-hot coke oven gases, it is to be understood that the invention is not limited by the drawing but that the process is also applicable to other coal distillation or coal carbonization gases and other similar hot gases containing pitchy or resinous ingredients which would be distilled or decomposed by the gases if allowed to collect on the tubes of an electrical precipitator thru which the gases passed.

in which the individual ovens are connected in the usual way thru uptake pipes 6 with a collector main 7. The gases from the ovens pass thru the uptake pipes and collector main thru the center-box 8 and the cross-over main 9 to condensers, and then to means for the recovery of ammonia, light oils, etc. This equipment which is of the usual type is shown schematically on the drawing.

At the back of the coke oven block several ovens which are connected with the collector main are also connected by means of pipes 10 to the top of an electrical precipitator 11. By suitable valve means in the uptake pipes 6 and the valves 12 in the pipes 10, the hot coke oven gases from these ovens may be directed either to the collector main or to the electrical precipitator.

This arrangement permits cleaning the hot coke oven gases at elevated temperatures, i. e., at temperatures at which the greater proportions of the tarry constituents in the gases are in vapor form e. g. at 350 C. to 500 C. By spraying the gases in the top of the precipitator thru sprays 13 with pitch which has previously been thrown out of the gases in the precipitator and which is recirculated from the bottom of the precipitator by means of the pump 13 thru the well insulated pipe line, entrained particles which are ordinarily present in the gases as they leave the ovens and which are precipitated on to the tubes of the precipitator are washed down off the tubes by the precipitation of the additional pitch sprayed into the gases without appreciable change in the temperature or composition of the gases. The electrical discharge passing between the electrodes causes entrained matter to precipitate in the upper portion of the tubes and near to the point at which the gases enter the tubes. The pitch is sprayed into the gases in such quantity that there is sufficient liquid thrown out of the gases on to the collecting electrodes of the precipitator to. provide a continual washing of the electrodes with the pitch. According to this invention the operation is carried out at such a high temperature that without the spray of pitch there would not be a continual washing of the tubes but stagnation of the precipitated matter on the tubes fol- I lowed by distillation or decomposition of this precipitated matter by the hot gases with consequent formation of hard pitch or coke on the tubes.

Where the tubes are well insulated or surrounded by a jacket of heating fluid such as super heated steam or hot combustion gases to prevent loss thru radiation, and where, for example, the gases are sprayed with pitchy material of the same temperature and composition as that carried by the gases so that the temperature or composition of the gases is not appreciably altered by the spraying and cleaning treatment, the cleaned gases will leave the precipitator thru the main 14 at a temperature only slightly less than the temperature at which the gases enter the precipitator. The temperature of the gases going thru the precipitator will be regulated so that the entrained matter 1. e. the pitch will be fluid at the temperature employed. At the temperature at which the gases leave the oven much of the entrained matter is in a dry state and would gases leaving the ovens, and even the vapors of higher boiling resinous constituents which are ordinarily condensed in the collector main and recovered with the tar, and which are condensed and removed from the gases together with the entrained impurities carried by the gases in any process for cleaning the gases except one in which the gases are treated at high temperatures such as those contemplated herein. I The type of precipitator shown comprises collecting electrodes or tubes 15 thru which discharge electrodes 16 are suspended. The discharge electrodes are connected to the bus-bar 1'7. Connecting the bus-bar to a source of negative unidirectional high potential current is made thru one of the chambers 18 or 19 in which the bus-bar is supported on suitable insulators. The

collecting electrodes 15 may be insulated against heat loss or the space surrounding the electrodes between the headers 18' and 19' and the shell of the precipitator may serve as a heating jacket thru which a suitable heating fluid is circulated thru the inlet 20 and out thru the'outlet 21. The upper and lower portions of the precipitator may advantageously be 'well insulated as indicated at 22. The piping leading from the ovens to the precipitator and from the precipitator to the condensers may also advantageously be well insulated where it is desired .to work at relatively high temperature.

When the gases are cleaned at temperatures not far below those at which, they leave the ovens and at which temperatures the entrained pitch is fluid and a separate clean condensate fraction comprising only high boiling oils or resinous constituents is desired, the gases are advantageously first treated in a condenser especially designed for condensing vapors of such high boiling compounds. Such high boiling compounds comprise high' melting point resins which if cooled in an ordinary condenser may freeze up and cause clogging of the tubes of the condenser and clogging of the outlet, etc. These gases are therefore advantageously first passed thru a suitable condenser to remove the resins, which may be termed a hot condenser, before being passed to ordinary condensers for theremoval of creosote oils and carbolic oils.

The condenser shown in Fig. 2 comprises two compartments 25 and 26 from which separate fractions may be separately withdrawn at 2'7 and 28. The lower portion of the condenser ,25 is the hot condenser in which the gases pass thru tubes 29 surrounded by a jacket thru which a warm or hot medium, such as steam or hot air, is passed, and in which the temperature of the gases is reduced only to a point which will cause condensation of the high boiling resins without condensinglower boiling constituents and at a temperature at .which the resins will remain liquid. The lower portion of the condenser is advantageous well insulated as indicated at 30. The gases from which the high melting point resins have been removed, are passed up thru the outlet 31 into an ordinary condenser 26 and there cooled to recover one or more separate fractions. The gases pass out from the condenser thru the precipitator and will rundown pipe 32 to means for recovering ammonia, etc., and may advantageously be united with the ordinary coke oven gases from the collector main 7 and treated with these gases in a common system for the recovery of ammonia and light oils, etc.,

Instead of spraying the gases with pitch of the same composition as that contained in the gases a tar or lower melting pitch, as. for=example, the tarry oil .ordinarly condensed from coke oven gases in the condensing system, may

be sprayed into the gases thru the sprays 13 before the gases enter the precipitator tubes and the gases caused to enter the tubes with particles of the tarry oil spray suspended therein. The tarry oil, which is more or less distilled by the hot gases, dissolves the heavy condensate precipitated from the gases on to the tubes of the precipitator. By spraying it into the gases in sufiicient quantity to flush the walls of the collecting electrodes and keep them clean, the accumulation of precipitate thereon is prevented.

The contact of the hot gases with the tarry oil spray and the large surface of tarry oil exposed to the gases as the oil flows down thru the tubes of the" precipitator, will cause more or -low boiling constituents may be sprayed into the gases to wash the tubes of the precipitator which will likewise be distilled to some extent by the hot gases. The term tar as used in the appended claim is therefore intended to include substances that contain tarry constituents and volatile oils, e. g. low melting pitches and tarry oils, as well as the total tar that is directly obtained from coke oven and similar gases. More or less distillation will result," depending upon 'the boiling point of the medium sprayed into the gases, the temperature of the gases, the time of contact, etc. On cooling gases which are en riched in condensable constituents volatilized from the material sprayed into the gases, a clean condensate is obtained which contains ingredients originally present in the gases as they leave the ovens and ingredients originally present in the material sprayed into'the gases. Blended products may thus be produced, the composition of which may be regulated by regulating the character andquantity of the material sprayed into the gases. 0

Although in'the drawing the precipitator is shown'as connected with the ovens thru special piping and the spraying means is shown in the top of the precipitator, the precipitator may be connected to the ovens in any'suitable way and any suitable spray devices may be provided in the pipes connecting the ovens with the precipitator or the gases may be collected in a suitable header and sprayed therein before entering the precipitator. Any'suitable manner of spraying the gases so that the gases enter the cleaning zone medium entrained therein, may be employed. It

will be understood that not all of the spraying medium will remain entrained in the gases. Some will settle out in the upper chamber of the thru the tubes, and aid in .flushing the tubes. 'Although the application is described more particularly as ap*- plied to the treatment .of .fresh hot coke oven gases, it may also be applied to the treatment of fresh hot retort gases or other hot gases containing pitchy or resinous constituents suspended therein.

I claim:

The method of treating fresh hot coal distillation or hot coal carbonization gases, which comprises spraying the gases with tar whereby distillation thereof is effected and. the residue from such distillation remains suspended in the gases, subjecting the gases with such residue suspended therein to an electrical discharge by passing them down thru the tubes of an electrical precipitator, whereby entrained matter is removed from the gases, and passing the gases enriched in condensable constituents volatilized from the 

